1. Field of the Invention
This invention relates to a photoelectric element
2. Description of the Prior Art
Improvement of the performance characteristics of photoelectric elements has been approached from various angles. Of particular note regarding techniques for enhancing the conversion efficiency of such an element by increasing its open-circuit voltage are those disclosed in Japanese Patent Laid Open No. 57-103371 and Appl. Phys. Lett., Vol. 54, No. 15, 1989, pp. 1460-1462.
The former of these teaches improvement of the open-circuit voltage and the fill factor of a SnO.sub.2 /Si heterojunction solar cell by a technique related to a method for depositing the SnO.sub.2.
The latter aims at achieving an efficiency improvement by forming junctions referred to as point contacts on the major surface of the substrate opposite the light-receiving surface (i.e. the rear surface) What this amounts to structurally is forming point-like P.sup.+ regions for junction formation at a prescribed pitch on the rear surface of a high-resistance n-type substrate and connecting the P.sup.+ regions of each row thereof by forming a plurality of stripe-like positive electrodes on the rear surface of the substrate. Moreover, stripe-like negative electrodes are formed interdigitedly adjacent to the stripe-like positive electrodes and good ohmic contacts are established between the negative electrodes and the high-resistance n-type substrate through point-like n.sub.+ contact regions formed at a prescribed pitch also on the rear surface of the substrate.
The method disclosed in the aforesaid Laid-Open Patent document focuses on improving the efficiency of the heterojunction itself and, as such, does not take the shape and layout on the light-receiving side of the element into consideration as factors in enhancing the open-circuit voltage and conversion efficiency.
On the other hand, while the teaching of the Appl. Phys. Lett. article aims at a structural improvement, the element structure that it proposes involves problems that derive from the fact that the positive and negative electrodes are present only on the rear surface of the substrate and that the two types of electrodes are formed alternately by connecting the members of each type with a plurality of stripes. For example, there is a high risk of shorting owing to thick solder joints, the adherence of electrically conductive foreign matter, and other such causes. The structure also has a drawback from the materials aspect. Specifically, since the current collection junctions are formed only on the rear surface of the substrate opposite from the light-receiving surface, the efficiency decreases, not increases, unless a material is used in which the carrier diffusion length is sufficiently greater than the substrate thickness.